AP Chemistry 1.4 Laws of Thermodynamics

If the temperature of A increases by 3 °C, and the temperature of B increases by 6 °C,

which of the following statements is true?

And here are our potential answers: These must be some creepy substances… [Gas appears]

Absorbing all this energy like dementors swallowing your soul… somebody should cast a patronus [Dementor appears]

charm, quick.

What's that?

Any object that increases in temperature is absorbing energy?

Oh….maybe we overreacted a little bit.

So to solve this problem, let’s take a look at this equation. [Finger points to equation]

Here, Q is the amount of heat or energy transferred when a material changes temperature, m is

the material’s mass, Cp is the heat capacity, and delta T is the change in

temperature.

We know from the problem statement that substances A and B have the same mass.

They also both absorb the same amount of energy, 50 joules.

That means the only factors that can differ between them are the change in temperature [Thermometer rising in temperature]

and the heat capacity.

So let’s write that out as an equation, which looks a little something like….this.

And even though it looks complicated, you don't have to be Hermione Granger to solve

this one.

The problem tells us the temperature increase for substance A is 3 degrees Celsius, while [Finger points to temperature increase for substance A]

the temperature increase for substance B is 6 degrees Celsius.

If we reduce this equation and cancel out the units, we can see that the heat capacity

of material A is twice the heat capacity of material B. And that just happens to be answer

choice (A).

Well done. [Girl pours potion]

You know, if you went to Hogwarts, we’re pretty sure you’d be a Ravenclaw, you smarty

pants.